The present invention relates to a data communication apparatus which can perform data communication such as the xDSL scheme using the telephone line for audio band communication.
In recent years, the xDSL communication system such as the ADSL (Asymmetric Digital Subscriber Line) communication system, the HDSL (High-bitrate Digital Subscriber Line) communication system and the SDSL (Symmetric Digital Subscriber Line) communication system which can perform high-speed digital communication of several Mbits/sec using the existing telephone copper cable have been closely watched as a wired digital communication system. One of the line codes in the xDSL communication system such as the DMT (Discrete Multi-Tone) modem system, is standardized by T1.413 of ANSI.
FIG. 7 shows a spectrum of the transmission signal of the DMT modem system. In this diagram, the band of 4 kHz or lower represents the normal telephone service constituting an audio band communication using the audio band, the band of 30 kHz to 320 kHz represents the up multicarrier wave for the ADSL communication of the DMT modem system, and the band of 30 kHz to about 1.1 MHz represents the down multicarrier wave for the ADSL communication of the DMT modem system. In the ADSL communication of the DMT modem system, the down multicarrier and the up multicarrier are overlapped and separated from each other by an echo canceller.
In the data communication apparatus of the DMT modem scheme such as the xDSL communication scheme, the data communication is normally preceded by a training for measuring the S/N ratio of the received wave for each channel. According to the measured values, the gain and the number of transmission bits are assigned to each subchannel. Thus, the gain and the number of transmission bits are determined according to the S/N ratio. Therefore, when the line attenuation is large or noises exist, the S/N ratio is decreased and the number of bits assigned is also reduced.
FIG. 8 shows an example of bit allocation in the case where the interference noises in the assembled-type line of the TCM-ISDN transmission path have an effect on the system. This diagram has been presented in the General Assembly (spring), the Institute of Electronics, Information and Communication Engineers, NTT, B-8-54, 1998, as xe2x80x9cInfluence of ISDN line on DMT based ADSL transmission characteristicsxe2x80x9d. As clear from this diagram, in the case where NEXT noises shown by dashed line are received as interference noises by the assembled-type line of the TCM-ISDN transmission path, the number of the transmission bits is allocated to each subchannel in such a manner that a frequency of low interference noises has a large bit allocation as indicated by solid line. The gain allocation, unlike the bit allocation, is normally carried out in such a manner that a large gain is allocated to portions with a large interference noise and a small noise to portions with a small interference noise.
In the data communication apparatus of xDSL communication scheme described above, however, the data communication is conducted using the telephone line for the audio band communication with a telephone set or the like. Therefore, the data communication service is unavoidably affected by the telephone service using the audio band. Thus, the characteristics of the telephone line is affected and differentiated between the on-hook state where the audio band communication is not conducted and the off-hook state where the audio band communication is being conducted.
FIG. 9 shows the frequency characteristic on the telephone line in the on-hook and off-hook states for the audio band communication. This was announced in AMD, D.176 (WP1/15) ITU-T SG15, Geneva, Feb. 9-20, 1998, as xe2x80x9cEmpirical Characterization of In-Home Telephone Wiringxe2x80x9d. As clear from this diagram, the gain level of the data communication conducted using the telephone line varies between the on-hook state and the off-hook state in audio band communication. This diagram shows that the gain varies considerably in the off-hook state where the audio band communication is being conducted using the telephone line, and as compared with the on-hook state where the audio band communication is not being conducted the gain characteristic is extremely deteriorated.
Assume that the training is conducted only in the on-hook state where the receiver is hung up to form a bit map for determining the bit allocation and gain of each channel or to conduct the coefficient training for adaptive equalization on the data communication apparatus side using the telephone line, so that the communication is conducted with the optimum bit allocation, the optimum gain setting and the optimum adaptive equalization filter for the particular telephone line. In the off-hook state where the receiver is picked up for audio band communication, the characteristics of the telephone line undergo a change. Thus, the problem is that each characteristic is no longer optimum, and the data transmission rate is required to be improved more without which an efficient communication becomes impossible.
The present invention has been developed to obviate these problems. It is an object of this invention is to provide a data communication apparatus in which data communication can be effected efficiently using the telephone line inspite of the characteristic change occurring between the on-hook state with the audio band communication not going on using the telephone line and the off-hook state where the audio band communication is being conducted data communication can be effected efficiently using the telephone line.
More specifically, when the data communication is not being conducted, the on-hook or off-hook state of the audio band communication is detected, and the characteristic of each state is trained. Thus, a table of the bit allocation, the gain setting, the adaptive equalization coefficient is prepared for each of the on-hook and off-hook states. During the data communication, the respective values are switched between the on-hook and off-hook states. Further, in the case where the telephone is not in use as the on-hook state is detected, the communication band is shifted or enlarged to the telephone service band.
The present invention provides a data communication apparatus for conducting the data communication using the telephone line for the audio band communication, characterized by comprising a detection unit for detecting whether the audio band communication is being conducted or not on the telephone line and a communication unit for conducting the data communication through the telephone line with the characteristics changed between the active audio band communication and the inactive audio band communication based on the detection output of the detection unit.
According to another aspect of the invention, the communication unit includes an active audio band communication coefficient table for storing the equalization coefficients when the audio band communication is being conducted on the telephone line, an inactive audio band communication coefficient table for storing the equalization coefficients when the audio band communication is not being conducted on the telephone line, and an equalizer for equalizing, based on the detection output of the detection unit, the receive signal of the data communication according to the audio band communication coefficient table when the audio band communication is being conducted on the telephone line, and the receive signal of the data communication according to the inactive audio band communication coefficient table when the audio band communication is not being conducted on the telephone line, characterized in that the noise removal characteristic is changed between the active audio band communication and the inactive audio band communication thereby to conduct the data communication through the telephone line.
According to still another aspect of the invention, the communication unit includes an active audio band communication bit allocation table for storing the bit allocation of each channel of data communication when the audio band communication is being conducted on the telephone line, an inactive audio band communication bit allocation table for storing the bit allocation of each channel of data communication when the audio band communication is not being conducted on the telephone line, and a bit allocator for allocating, based on the detection output of the detection unit, bits to each channel according to the active audio band communication bit allocation table when the audio band communication is being conducted on the telephone line, and bits to each channel according to the inactive audio band communication table when the audio band communication is not being conducted on the telephone line, characterized in that the bit allocation characteristic to each channel is changed between the active audio band communication and the inactive audio band communication thereby to conduct the data communication through the telephone line.
According to a further aspect of the invention, the communication unit includes an active audio band communication gain allocation table for storing the gain allocation of each channel of data communication when the audio band communication is being conducted on the telephone line, an inactive audio band communication gain allocation table for storing the gain allocation of each channel of data communication when the audio band communication is not being conducted on the telephone line, and a gain allocator for allocating, based on the detection output of the detection unit, the gain to each channel according to the active audio band communication gain allocation table when the audio band communication is being conducted on the telephone line, and the gain to each channel according to the inactive audio band communication table when the audio band communication is not being conducted on the telephone line, characterized in that the gain allocation characteristic to each channel is changed between the active audio band communication and the inactive audio band communication thereby to conduct the data communication through the telephone line.
According to a still further aspect of the invention, there is provided a data communication apparatus for conducting the data communication using the telephone line for audio band communication, characterized by comprising a detection unit for detecting whether or not the audio band communication is being conducted on the telephone line, and a communication unit for conducting, based on the detection output of the detection unit, the data communication using a predetermined band not interfering with the audio band communication at the time of active audio band communication, and the data communication using up to the neighborhood of the audio band interfering with the audio band communication at the time of inactive audio band communication.
According to a yet further aspect of the invention, there is provided a data communication apparatus for conducting the data communication using the telephone line for audio band communication, characterized by comprising a detection unit for detecting whether or not the audio band communication is being conducted on the telephone line, and a communication unit for conducting, based on the detection output of the detection unit, the data communication using a predetermined band not interfering with the audio band communication at the time of active audio band communication, and the data communication using up to the audio band at the time of inactive audio band communication, the communication unit including, on the transmitting end alone, a filter for removing the frequency band of the ring tone signal for transmitting an audio band communication request to the receiving end.
According to a still further aspect of the invention, there is provided a data communication apparatus characterized in that the data communication is the ADSL data communication of discrete multitone modem scheme, and the apparatus is an ADSL communication modem.